Rapid photographic developing



y 7, 1963 J. H. JACOBS 3,088,824

RAPID PHOTOGRAPHIC DEVELOPING Filed Feb. 17. 1959 INVEN TOR. JOl-M/ H J14 (056' United States Patet O 3,088,824 RAPE) PHQTOGRAPHIC DEVELOPING John H. Jacobs, Altadena, Calif, assignor, by mesne assignments, to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Filed Feb. 17, 1959, Ser. No. 793,727 4 Claims. (Cl. 9663) This invention relates to a high speed processing solution for developing photosensitive emulsions, and has great utility for rapid access photographic recording.

As dynamic recording has increased in application and importance, there have evolved fields of use in which a very short access time is desirable. The term access time is used to indicate the time interval between the exposure of a photosensitive recording paper to a light stimulus to be recorded and the presentation of the resultant record for visual observation. The terms photographic paper and recording paper are used throughout the specification and claims to include photosensitive emulsions disposed in any suitable support such as paper, film or other usable medium.

Wind tunnel and flight testing are examples of procedures where rapid access is of considerable value. Quick inspection of recorded data improves efficiency in changing conditions of operation to obtain additional necessary data. Moreover, test results can be recorded and visually observed in a brief, rather than a prolonged, interval of time.

Previous conventional photographic recording techniques generally referred to as oscillography have involved the exposure of an entire roll of a record paper to the information to be recorded with subsequent and separate chemical development of the roll thus exposed. In this procedure a record roll of say approximately 25 4-00 feet in length is entirely exposed before its removal from the oscillographic recorder and its subsequent development by conventional means. This prior procedure requires a rather long access time of minutes or even hours.

Copending application Serial No. 681,804, filed September 3, 1957, owned by the same assignee, describes and claims a high speed developing process which perm-its visual access of a photographic record in less than one second after exposure. This is accomplished by moving a strip of photographic recording paper through a film magazine at high speed past a spot of light which moves in accordance with the signal to be measured. As soon as the paper moves past the light spot, the emulsion on the paper is wetted With a thin film of a high speed alkaline processing solution, which is almost immediately dried as the paper passes over a hot platen. The dried, developed record emerges from the magazine within one second after exposure.

The invention of the co-pending application produces a record with very short access time, but the record has dried developer salts on its surface, and tends to darken or stain if it comes in contact with moisture, say due to high humidity or finger prints. The record can be stabilized with a fixing solution, but this requires an additional step, and if done in the magazine, increases instrumentation cost and access time.

The present invention reduces or eliminates the problem of record darkening or staining by using a processing solution which includes a thermally unstable alkali so that when the record is exposed to heat, the alkali is decom- 3,088,824 Patented May 7, 1963 posed or vaporized, causing the alkalinity of the solution to decrease to a point where the developing activity of the solution is substantially reduced, or eliminated. Thus, even if the developed record is subsequently exposed to moisture, the alkalinity of the emulsion surface is so reduced that further darkening or staining is either substantially reduced, or entirely prevented.

Briefly, the invention contemplates the method of rapidly developing a photosensitive emulsion with an alkaline processing solution containing a thermally unstable, or fugitive, alkali. The emulsion is exposed to light, Wetted with the solution to develop the exposed portion, and thereafter heated to decompose or drive off the unstable alkali.

In the presently preferred practice, the unstable alkali is an ammonium compound, such as ammonium hydroxide, or a substituted ammonium hydroxide. The preferred practice also uses a recording paper with an emulsion which includes a compound that becomes acid when heated, so that the dried developer salts remaining on the emulsion are not merely made less alkaline when heated, but are left potentiallyacidic to further decrease the developing activity of the remaining salts.

The invention can be practiced with conventional processing solutions which include thermally stable alkalis, such as sodium hydroxide or sodium carbonate. In such cases, an ammonium salt, say ammonium chloride, is added to the conventional alkaline processing solution to form the thermally unstable alkali, ammonium hydroxide.

The term processing solution is used throughout the specification and claims to designate primarily a developing solution, but the solution may also include various additives such as silver halide stabilizers or solvents, and the like.

The developing procedure generally outlined above can be done substantially simultaneously with the exposure of the recording medium to the light to be recorded. The processing solution may be applied as a thin film directly after such exposure or even prior thereto, but it is desirable that exposure precede the application of heat as described.

Preferably, only a very thin film of the processing solution is used on the recording medium. By limiting the thickness of the applied film so that substantially only the emulsion is moistened, this film preferably being not in excess of .0005 inch and preferably in the neighborhood of .0002 to .0003 inch thick, drying is facilitated, and the record, by reason of its dry back surface, may be immediately passed over a stationary hot platen with a minimum of distortion or wrinkling, which could impair heat transfer from the platen into the record. Since it is preferred that the record be substantially dry before exposure to ambient light conditions for visual observation, the importance of the thin film principle in permitting very rapid drying speed is obvious. Moreover, the thin film reduces the amount of heat required to produce a thorough degeneration of the unstable alkali, which results in a comparatively stable developed record.

One form of apparatus for performing the steps of the invention is shown in schematic elevation in the accompanying drawing.

Referring to the drawing, a record handling unit 9 is enclosed in a magazine 10 having on one side a window 11 through which a light beam 12 produced in a conventional recording camera enters the magazine. The camera is illustrated schematically as a light source 13 and a modulator 'represented as a galvanometer mirror. Thecamera as such form-she part-of the present invention and is conventional in the process of oscillography. 'In the usual commercially employed oscillograph a number of channels of data may be recorded at the same time by using a plurality of light modulators and recording the modulations responsive to separate signals applied to the respective modulators and representing a plurality of parameters to be recorded.

Typically, a plurality of pressure transducers may be incorporated in various locations of awind tunnel with their outputs separately connected to a different one of a plurality of galvanometers in a multi-channel oscillograph. For the purposes of describing the invention a single galvanometer mirror 14 is shown as illustrative of the phenomena involved with the invention, and is representative of any number of separate channels of recordmg.

The magazine 10 houses a supply roll 16 on which an unexposed strip of recording medium 17, say photographic recording paper, .is stored. The record is carried over a metering roller 18 driven by conventional roller drive means (not shovm) to determine the speed of travel of the recording medium through the magazine. The metering roller is adjacent the magazine opening so the light beam strikes the photographic emulsion (not shown) on the paper as it passes over the metering roll. From the metering roller the record is carried around an idling or tension roller 19 and from there past a processing solution applicator 20.

The applicator 20 as shown schematically in the drawing comprises a processing solution reservoir 21, a socalled slit applicator 22 which communicates at one end with the reservoir 21 and is open through a narrow slit (not shown) at another end, which bears against the recording paper 17 as it is stretched across a mandrel 23. Any type of solution applicator can be used, but best results are obtained when the processing solution is applied as a thin film which wets only the emulsion, and not the paper backing of the recording medium. As presently preferred in the practice of this invention, I use a novel slit type applicatorwhich applies an even film of solution without pumping means, andwhich is generally insensitive to variations in record speed. The particular applicator illustrated schematically herein is described in detail and separately claimed in co-pending application, Serial No. 712,148, filed January 30, 1958, by Michael D. Godfrey, and owned by the same assignee.

A further benefit of using a thin film is the many-fold reduction in consumption of processing solution over that required in conventional developing procedures. An entire roll of photographic recording paper amounting to approximately 400 square feet can be processed with no more than 400 cubic centimeters of processing solution. The same roll processed by conventional procedure of paper dipping would not only take about 10 to lOO times the access time as emphasized above, but would involve the consumption of approximately 900* cubic centimeters of solution. A still further advantage of this film application of processing solution is that the developer in supply reservoir 21 remains always at full strength, there being no gradual exhaustion of developer in the process of developing a roll of paper aswould be the-case if the paper were immersed in the developer.

The latent image produced in the recording medium at the instant of exposure through window 11 would not be rapidly developed after application of the processing solution at the applicator 22. without further impetus. However, at this point, the record cannot be exposed to ambient lightsincethe emulsion is highly active while it is damp with developer. Accordingly, the. crux of rapid-accessis the. application of large quantities of heat relative to the amount of. developer present to induce rapiddevelopment and simultaneous drying and'reduc- 4 tion of the alkalinity of the thin film of developer. This isfacilitated when a small volumeof-developer is'used and the recording paper itself has not been wet.

To achieve fast heating of the wetted emulsion, the paper is carried from the applicator 20 over a guide roller 24 and across a curved face 25 of a heated platen 26. The dimensions of the platen are selected to achieve the desired degree of drying at the ranges of paper speed to be encountered and under acceptable conditions of temperature. Generally speaking we have found that the record can be dried at a temperature in excess of about C. and preferably in the neighborhood of C., requiring a drying time of approximately 0.4 second. At this point, the thermally unstable alkali is either decomposed or driven off-so that the alkalinity of the processing solution (or the potential alkalinity of the dried salts remaining on the emulsion) is substantially lowered, thereby reducing the potential developing activity of the dried salts, if they should again become moist.

The platen 26 may be heated in conventional fashion by insert heaters (not shown). To accomplish the rapid drying desired it is necessary to transfer relatively large quantities of heat to the record. This can be accomplished by high power input to the platen, but preferably is done by causing the platen to act as a heat sink storing relatively large amounts of heat developed at comparatively low power consumption during periods of inactivity, e.g., while the record roll is being changed. Any form of heated platen may be employed, there being many adequate to apply the necessary heat to the record.

From the platen the record is passed through compression rolls 27, 28, the roller 27 being driven through a slip clutch to maintain a constant tension on the record strip between the metering roll 18 and the point of the compression rollers. Thereupon the record is discharged from the magazine through an exit slit 29.

Using a processing solution in accordance with this invention, the record obtained from the magazine is sufiiciently stable to permit leisurely visual observation without significant subsequent staining or darkening. 'It is the general experience that a large percentage of the records produced in the testing procedures in which oscillographs are employed are of no permanent value, and once observed to evidence the conditions under investigation may be destroyed. As related to this large percentage of total record which is to be destroyed, the rapid processing technique, which eliminates the more time consuming treatment in stabilizing solutions, has not only the advantage of quick access, but further eliminates stabilization of records which have no permanent value. At the same time, the record is of sufiicient permanence that any segments of prolonged or permanent value may be selected and separately processed minutes, hours or days later for ultimate and complete stabilization if required. At this point, the time required to stabilize is of no concern since the record has already been observed and has thus served its immediate purpose.

In addition to a thermally unstable alkali, the processing solution used with this process preferably has other special characteristics. In particular, it should not fog the sensitive layer at the high temperatures used for rapid development and drying. This problem is especially severe when the traveling speed of the recording medium is varied over a Wide range. The oxidation products of the processing solution should preferably be colorless. Further, the developer components or'their pyrolysis and oxidation products should not react with constituents of the photosensitive layer or its support (for instance, the sensitizing dyes to be found in most photographic emulsions) to form markedly colored products. This being so, and bearing in mind the diversity of the constituents which may be used in photographic media, optimum results are achieved by formulation of a particular developer to work with a desired type of photographic recording medium.

My co-pending application, Serial No. 699,601, filed November 29, 1957, describes and claims a developing solution which develops recording paper over a wide range of paper speeds without fogging. However, this developer uses a conventional thermally stable alkali, and the record is subject to darkening and staining.

The following Table I gives the range of composition by weight of one group of components which make processing solutions with a thermally stable alkali for use in accordance with this invention:

Table I Gm. Sodium sulfite (anhyd.) 10-150 Phenidone -18 Chlor-hydroquinone 5-18 Caustic soda 17-36 Ammonium chloride 22-48 Benzotriazole 2-18 Potassium bromide 1-9 Water to 1000 ml.

paper mentioned in the paragraph preceding Table I is shown in the following Table II:

Table II Sodium sulfite (.anhyd.) gm 75 Phenidone gm 6 Hydroquinone, or chlor-hydroquinone, or mixture gm 6 Caustic soda gm 18 Ammonium chloride gm 23 Benzotriazole gm 6 Potassium bromide gm 3 Teepol (stock solution) ml 20 Water to 1000 ml.

Solutions made in accordance with Table I or II preferably have a pH of 12-13. Any suitable alkali, or mixture of alkalis, can be used as well as caustic soda. For example, sodium or potassium carbonate can also be used.

As a significant example of effectiveness of the described processing solution, it may be compared with the operation of a presently available commercial oscillograph. In the present instruments paper transport speeds of 2 to 100 inches-per-second or more are possible but the record is made in a detachable magazine which must be taken from the recorder to a dark room and processed in the usual manner. Under ideal circumstances the record may be available for visual examination within approximately 10-20 minutes after exposure. At the slower recording speeds and with records of approximately 250 feet in length there must be added to this time for visual observation of the initially exposed portions the time consumed in exposing the entire record. By employing the present high speed technique and processing solution, any portion of the record is visible in an interval determined only by the time required to travel from exposure to discharge, this being a function of the length of record in residence between the point of exposure and the outlet window of the magazine and the paper speed involved. At recording speeds in excess of about 25 inches per second an access time of less than 0.8 second is realized, and the record is resistant to staining or streaking, even if exposed to moisture.

The following Table III gives the composition by weight of another group of components which make processing solutions with a thermally unstable alkali for use in accordance with this invention:

Table III Hydroquinone 10 Phenidone (define) 2 Sodium hydroxide 5 Sodium carbonate Ammonium chloride 24 Sodium sulfite (anhyd) 30 Benzotriazole 4 When the thermally unstable alkali is formed in the developer solution by the addition of an ammonium salt to react with the alkali already in solution, as in the foregoing examples of Tables I-III, unstable alkali is formed as follows:

NaOH+NH Cl, NaCl-l-NH OH On heating, the following occurs:

NH OH- NH +H O The ammonia escapes as a gas and the pH of the developer drops, thereby reducing its activity.

Ammonium salt addition is satisfactory for those cases in which the developing solution on hand already has a high alkalinity, say due to the presence of a thermally stable alkali such as sodium hydroxide. However, it has the disadvantage of increasing the salt content of the solution, which adds to the non-volatile materials to be absorbed by the record paper.

The total salt content may be reduced by combining the fugitive alkali function with that of the preservative (sodium sulfite) by using ammonium sulfite instead of the chloride. The first reaction is then:

SO :Na SO On heating, the reaction is:

NH3 H2O Again the :alkalinity is destroyed, but the use of sulfite ions makes it unnecessary to use sodium sulfite in the original formulations of Tables I-III, in which case the (NH SO replaces the NH Cl in the ratio of their molecular weights N z s s s s z OH N 3) a s z) 3 N 2 5 2 c s z 2 Each of the foregoing decompose on heating, causing the solution alkalinity to drop. The :above list could be extended almost indefinitely to include entire homologous series, isomers, and organic radicals similar to those listed above. In general, the quaternary ammonium hydroxides a-re strong bases with ionization constants about that of sodium hydroxide. These compounds decrease in thermal stability as the substituted organic radicals increase in size and complexity. Tetraethyl ammonium hydroxide is less stable than tetramethyl ammonium hydroxide, and tetrabenzyl ammonium is so unstable that it apparently has never been isolated.

Whatever thermally unstable alkali is used, it replaces the alkali and ammonium chloride of the examples given 7 in Tables IHI approximately; in accordance with the following formula:

M.W. of unstable alkali M.W. of ammonium chloride Xvvt. of ammonium chloride The desired end in each case is to have the pH of the solution, before processing, between about 1213. Of course other alkaline developers may be used, and the amount of thermally unstable alkali is merely adjusted to give the desired initial pH.

The decomposition of the thermally unstable alkali may bring the system to neutrality, but can take it no further. To improve the protection of the record in some cases from staining by oxidized developer; it is desirable to bring the system into an acid condition. This is done by incorporating a material such as zinc sulfite into the recording paper base, or into a layer close to the The sulfur dioxide is an acid gas, i.e., forms an acid when dissolved in water, and acidi-fies the emulsion layer. If traces of water are still present at this stage, the sulfur dioxide is absorbed by the sodium sulfite to form sodium bisulfite. The complete reaction is represented by:

211803 N32SO3 When in solution, sodium bisulfite givesa pH of around 5. That is, the record is now in an acid condition. This prevents further development and minimizes staining due to the oxidation of developer.

Other materials which can be included in the paper base, and which will liberate an acid gas on heating are a the sulfites, sulfates, and carbonates of such metals as zinc, mercury, tin, and lead. Still other examples are the hydrochlorides of high molecular weight stable organic bases, such as cyclohexylamine hydrochloride and its higher homologs. These materials may also be incorporated into the paper base, where they will liberate hydrochloric acid gas when heated. All of the foregoing examples are stable at temperatures above 100 C.

To facilitate an understanding of this unique photo'- graphic processing solution, it has been described as applied to the field of dynamic recording. It is evident from a familiarity with the widespread efforts now' being made to achieve rapid record access that this solution represents a major advance in this field. However, the processing solution is in no Way limited in its usefulness to dynamic recording and the detailed description of such application should not be so construed.

I claim:

1. A photographic recording medium comprising a support containing cyclohexylamine hydrochloride, and a sliver halide photosensitive emulsion disposed on the support.

2. The method of rapidly developing a silver halide photosensitive emulsion on one side of a support with an alkaline developer'solution forthe silver halide emulsion containing an alkali thermally unstable between about above the range of about C. to about C., the

method comprising exposing the emulsion to light, wetting the emulsion with a thin film of the developer and alkali solution while maintaining the opposite side ofthe support dry, thereafter heating the wetted emulsion to drive off the unstable alkali and lower thepH of the solution on the emulsion, whereby the developing activity of the solution is decreased, and thereafter heating the support sufficiently to decompose the saidcompound to produce an acid gas.

3. The 'methodof rapidly developing a silver halide photosensitive emulsion on-one sideof a support with an alkaline developer solution for the silver halide emulsion containing-an alkali thermally unstable between about 90 C. and-about120 C.-, the support alsocarrying zinc sulfite, the method comprising exposing the emulsion to light, wetting the emulsion with a thin film of the developer and alkali solution while maintaining the opposite side of the support dry, thereafter heating the wetted emulsion to drive oif the unstable alkali and-lower the pH of the solution on the emulsion, whereby the developing activity of the solution is decreased, and heating the support sufficiently to decompose the zinc sulfite and liberate sulfur dioxide.

4. The method of rapidly developing a silver halide photosensitive emulsion on one side of a support with an alkaline developer solution for the silver halide emulsion containing an alkali thermally unstable between about 90 C. and about 120 C., the support also carrying an inorganic salt madefrom a metal selected from the group consisting ofzinc, .tin, lead, and mercury, and combined with a radical selected from the group consisting of sulfite, sulfate, and carbonate, the method comprising exposingthe emulsion to light, wetting the emulsion with a thin film ofthe developer and alkali solution while maintaining the opposite side of the support dry, thereafter heating the wetted emulsion :to drive olfthe unstable alkali and lower the pH of the solution on the emulsion, whereby the developing activity of the solution is decreased, and heating the inorganic salt sufiiciently to decompose it and release an acid gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,819,848 Simjian Aug. 18, 1931 2,057,764 Brunken Oct. 20, 1936 2,179,790 Jones et al Nov. 14, 1939 2,618,556 Hewitson et a1. Nov. 18, 1952 2,839,405 Jones June 17, 1958 2,922,352 Tuttle et al. Jan. 26, 1960 2,930,302 Tuttle Mar. 29, 1960 FOREIGN PATENTS 811,227 Australia July 4, 1927 647,922 Great Britain Dec. 28, 1950 OTHER REFERENCES Henney et'a1.: Handbook of Photography, Whittlesey House, N.Y., 1939, pp. 334, 340, 341. 

2. THE METHOD OF RAPIDLY DEVELOPING A SILVER HALID PHOTOSENSITIVE EMULSION ON ONE SIDE OF A SUPPORT WITH AN ALKALINE DEVELOPER SOLUTION FOR THE SILVER HALIDE EMULSION CONTAINING AN ALKALI THEREMALLY UNSTABLE BETWEEN ABOUT 90*C. AMD ABOUT 120*C., THE SUPPORT ALSO HAVING A THERMALLY UNSTABLE COMPOUND WHICH RELEASES AN ACID GAS ABOVE THE RANGE OF ABOUT 90*C. TO ABOUT 120*C., THE METHOD COMPRISING EXPOSING THE EMULSION TO LIGHT, WETTING THE EMULSION WITH A THIN FILM OF THE DEVELOPER AND ALKALI SOLUTION WHILE MAINTAINING THE OPPOSITE SIDE OF THE SUPPORT DRY, THEREAFTER HEATING THE WETTED EMULSION TO DRIVE OFF THE UNSTABLE ALKALI AND LOWER THE PH OF THE SOLUTION ON THE EMULSION, WHEREBY THE DEVELOPING ACTIVITY OF THE SOLUTION IS DECREASED, AND THEREAFTER HEATING THE SUPPORT SUFFICIENTLY TO DECOMPOSE THE SAID COMPOUND TO PRODUCE AN ACID GAS. 